Mitochondria cannot be synthesized de novo; instead, newly-formed daughter cells must inherit their mitochondria from the mother cell during division. Although the metabolic functions of mitochondria have been extensively studied, very little is known about the molecular mechanisms controlling mitochondrial transmission. Recently, an important class of genes (termed MDM for "mitochondrial distribution and morphology") has been identified through the use of temperature-sensitive mutants that disrupt mitochondrial inheritance during yeast budding. The precise functions of these gene products are not yet understood. All but two of these MDM genes are represented by single mutant alleles suggesting that additional components of the mitochondrial partitioning apparatus remain to be identified. We have identified eight new genes that are required for mitochondrial transfer into newly formed daughter cells during east budding. We propose to study the molecular basis of mitochondrial partitioning in yeast via the genetic, molecular and biochemical characterization of these 8 new MDM genes and the proteins they encode. FIRST, we will use a combination of vital staining, indirect immunofluorescence, and electron microscopy to characterize the range of mitochondrial inheritance and morphology defects caused by mutations in MDM genes. SECOND, wild-type and mutant alleles of the 8 MDM genes will be cloned, sequenced and analyzed. This analysis will allow us to identify any important structural motifs and functional domains in the predicted proteins. THIRD, we will use indirect immunofluorescence and cell fractionation experiments to determine the subcellular location of Mdm protein. FOURTH, we will analyze mitochondrial partitioning during meiosis in mdm mutants. These studies will allow us to determine whether Mdm proteins mediate mitochondrial movements during both meiosis and mitosis and may reveal details of mitochondrial partitioning that cannot be easily visualized in mitotically dividing cells. The experiments we propose will lay the foundation for future molecular, biochemical and genetic analyses of Mdm protein function. In the long- term, these studies should contribute to our basic understanding of the molecular mechanisms underlying mitochondrial movements during cell division and during early development in other organisms.